Production of viral vectors for vaccines poses a distinct set of challenges. Tony Hitchcock, head of manufacturing at Cobra
Biologics, spoke with BioPharm International about trends and challenges of manufacturing viral products in cell culture.
BioPharm: With the approval of Novartis' mammalian cell-produced influenza vaccine in 2012, production methods for viral vaccines seem
to be undergoing a shift from egg-based manufacturing to cell-based. What advances in recent years have enabled this transition
and what challenges still remain?
Hitchcock: The production of viral vaccines has been performed in egg-based systems for many years, and it is clear that while significant
developments in the production of viral vectors from cell culture-based systems have advanced, many existing vaccine products
will continue to be produced in this manner. For example, GlaxoSmithKline has just introduced a quadravalent flu vaccine from
eggs, and Medimmune has invested significantly in the automation of egg-based processes at their UK facilities. These developments
would indicate that for products, such as seasonal flu vaccine, existing production routes will be retained for the foreseeable
For manufacturers of products such as flu vaccines, while significant investment from national governments among others has
been put in place to develop cell-based production process to enable response to pandemic flu, it is clear that egg-based
processes are still sufficiently productive and cost effective to meet needs for seasonal demand. Combined with long-term
safety profiles and in-place manufacturing capabilities, the drivers for adopting cell-based processes are not sufficient
to justify their adoption. It is also clear that because of the specialist nature of egg-based production facilities, the
majority of manufacturing will remain as an in-house activity with limited opportunities for contract manufacturers in this
In January 2013, however, FDA approved Protein Science Corporation's Flublok vaccine, another non-egg-based influenza vaccine,
which is potentially the sign of things to come. It will be interesting to see what the up the uptake of this product will
be compared with the existing egg-based products, and how the large Pharma companies respond to this.
The real opportunities for the production of viral vectors from cell culture-based processes arguably lie with novel vaccine
products, where there are no historical safety profiles in place. Other opportunities lie with products where egg-based systems
are unsuitable, or where technical or product safety issues mean alternative approaches need to be sought to meet demands
in terms of quantities of material or to achieve required levels of process robustness.
BioPharm: What are the risks associated with using cell-based manufacturing for vaccines, and how are these risks typically addressed?
Hitchcock: The potential risks with cell-based processes can be split into intrinsic and process related. In terms of intrinsic risks,
these will lie with the origin, purity, and design of the viral vector and producer cell line. Process-related risks will
lie with the potential to introduce adventious agents/viruses into the process stream. Unlike the production of protein products
from mammalian sources, it is clearly not possible to introduce validated viral inactivation or removal steps to mitigate
these risks. Addressing these requires application of GMP principles and approaches to development programs at a very early
stage, focusing on the history, purity, and stability of the viral vector. It is now commonplace for viral vectors to be rescued
from synthesised plasmids, allowing for absolute traceability of the viral vector and full sequencing to be performed of the
plasmids and resulting viral product. Stability studies can also be performed to demonstrate genetic stability of vectors
at an early stage of development.
With regards to producer cell lines, it is essential that the origins are known and that they are free from adventious agents
and that generation of cell banks for both process development as well as GMP production works. Additionally, there is clearly
a need for maintenance of segregation throughout development programmes to prevent contamination of viral stocks and cell
BioPharm: How do you address the demands of producing such a diverse product? Are there aspects of the production process that are
Hitchcock: From the perspective of a contract development and manufacturing organization, the production of viral vectors poses a number
of technical challenges from a cell culture, recovery, and analytical perspective. However, with recombinant viral vector
systems, where the virus is essentially used as a delivery vehicle and the manufacturing approach that applies is independent
of the gene payload it carries, a platform process can be developed. Therefore, the application of platform-based approaches
can be applied for the production and analysis of key virus product areas, such as adenovirus, AAV, and lentiviral production.
BioPharm: Have you been able to implement quality-by-design (QbD) in your vaccine manufacturing process? Are there aspects of the production
process that are more amenable than others to this approach?
Hitchcock: The complexity of these product types and the limitation of assays to be able to fully characterize them means that understanding
and control of the manufacturing process is crucial to be able to develop, scale, and manufacture high-quality therapeutic
products. Therefore, the determination of the "operational space" for key process steps is essential. Where possible, there
is clear merit in adopting a QbD approach. However, especially in early phase development, there are often severe restrictions
created by assay throughput and for some virus types such as lentivirus produced by transient expression systems, there is
often very limited material available for high-throughput development platforms for use in purification and formulation studies.
In other product types, such as those like adenovirus produced in suspension culture, there are fewer constraints with regards
to material availability, and it is much easier to apply these approaches through all stages of development.